Is this stock '04 Silverado ext. cab a 4.8? 5.3? 6.0? 2WD? 4WD?
What kind of race- 1/4 mile? 1/8 mile? Until one of you clearly pulls the other? From a dig or rolling?
I'd say you have this one in the bag, unless yours isn't running like it should. Still, do everything you can to maximize your chances. Between running it for a while on the E85 (to allow it to fully adjust) and on a 1/4 tank to minimize the weight, I'd say you have a good handle on this already. Lose the third row seats if you haven't already. Be safe, have fun and good luck!
Oh- I don't think it'd be a total ass-whoopin', but I'm gonna place my bet on you. I'm gonna say you'll pull him by at least a car length.